File Encryption and Decryption in C#

Introduction

This article demonstrates how to use C# to encrypt and decrypt files of any type.

Background

Recently I needed to find a simple to way to encrypt and decrypt a file of any type (I actually needed to encrypt image and text files) and any size. I found hundreds of examples on the web, many of which just plain didn't work, or threw errors on certain file types.

Eventually I put together the following two methods using the Rijndael encryption algorithm, they simply require that you pass them the full path to the original and target files. They both require the System.Security, System.Security.Cryptography, System.Runtime.InteropServices and System.Text.RegularExpressions namespaces.

Unfortunately, as I looked at so many examples on the web and actually did all this a while ago, I do not remember which bits of code were orginally written by who. So if you recognise some of it, many thanks, leave a comment below so that your work doesn't go unrecognised.

Using the code

There are two methods: encryptFile and decryptFile. They both require that you pass in the filenames and paths of the source and destination files as strings. It is important that the user has the necessary files rights to create the encrypted file.

        ///<summary>
        /// Steve Lydford - 12/05/2008.
        ///
        /// Encrypts a file using Rijndael algorithm.
        ///</summary>
        ///<param name="inputFile"></param>
        ///<param name="outputFile"></param>
        private void EncryptFile(string inputFile, string outputFile)
        {
 
            try
            {
                string password = @"myKey123"; // Your Key Here
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(password);
 
                string cryptFile = outputFile;
                FileStream fsCrypt = new FileStream(cryptFile, FileMode.Create);
 
                RijndaelManaged RMCrypto = new RijndaelManaged();
 
                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateEncryptor(key, key),
                    CryptoStreamMode.Write);
 
                FileStream fsIn = new FileStream(inputFile, FileMode.Open);
 
                int data;
                while ((data = fsIn.ReadByte()) != -1)
                    cs.WriteByte((byte)data);
 
                
                fsIn.Close();
                cs.Close();
                fsCrypt.Close();
            }
            catch
            {
                MessageBox.Show("Encryption failed!", "Error");
            }
        }
        ///<summary>
        /// Steve Lydford - 12/05/2008.
        ///
        /// Decrypts a file using Rijndael algorithm.
        ///</summary>
        ///<param name="inputFile"></param>
        ///<param name="outputFile"></param>
        private void DecryptFile(string inputFile, string outputFile)
        {
 
            {
                string password = @"myKey123"; // Your Key Here
 
                UnicodeEncoding UE = new UnicodeEncoding();
                byte[] key = UE.GetBytes(password);
 
                FileStream fsCrypt = new FileStream(inputFile, FileMode.Open);
 
                RijndaelManaged RMCrypto = new RijndaelManaged();
 
                CryptoStream cs = new CryptoStream(fsCrypt,
                    RMCrypto.CreateDecryptor(key, key),
                    CryptoStreamMode.Read);
 
                FileStream fsOut = new FileStream(outputFile, FileMode.Create);
 
                int data;
                while ((data = cs.ReadByte()) != -1)
                    fsOut.WriteByte((byte)data);
 
                fsOut.Close();
                cs.Close();
                fsCrypt.Close();
 
            }
        }